AutoBlock is a 3D CAD-based program for investigating stability problems of slopes and foundations (e.g. dam abutments) in rock. It can import arbitrarily complex terrain surfaces which have been digitized beforehand using a topographic map. The surfaces are then extruded to 3D solids which are intersected by all possible locations of various sets of discontinuities. This leads to kinematically possible potentially unstable blocks, for which, based on limit equilibrium conditions, the safety may be computed. All investigations are carried out with Digital Terrain Models which represent arbitrarily complex terrain surfaces, and all results may be visualized within AutoCAD. In this way it is possible to recognize critical areas and to execute parametric studies.